Tris(bipyridyl)ruthenium(II)-photosensitized reaction of 1-benzyl-1,4-dihydronicotinamide with benzyl bromide

An NADH model compound, 1-benzyl-1,4-dihydronicotinamide (BNAH), reduces benzyl bromide to yield toluene as the main product under irradiation of the absorption band of BNAH in the presence of pyridine in acetonitrile, while the addition of a sensitizer tris(bipyridyl)ruthenium(II){[Ru(bpy)3]2+} to the BNAH-benzyl bromide system results in a drastic change in the photoreduced products, yielding 1,2-diphenylethane as the main product. Photosensitization by [Ru(bpy)3]2+ has been shown to change the mechanism of the photochemical reaction of BNAH with benzyl bromide; reaction in the absence of [Ru(bpy)3]2+ proceeds by a radical chain mechanism involving benzyl bromide. However, the [Ru(bpy)3]2+-mediated photoreduction of benzyl bromide with BNAH occurs in the presence of [Ru(bpy)3]2+, where benzyl bromide is subject to two-electron reduction by [Ru(bpy)3]+ which is formed by an electron transfer from BNAH to the excited state of [Ru(bpy)3]2+.